Look kid, you are putting me on the spot here but since you asked I'll tell you.

Yoda and I were too old so we needed you to knock off Darth Vader for us. We figured that if you knew he was your father you wouldn't do it. So, I kinda left that part out when I stated teaching you about the force and all that. It's a little sneeky, I admit, but I did what I had to do.

We've all done things we aren't proud of. I didn't tell you the whole truth about your father. You made out with your sister. What can you do, shit happens.